Electric fence barrier systems are well known in the industry for, amongst other applications, preventing unauthorised entry into a protected zone (or to retain animals within a confined area).
With reference to FIG. 1, an electric fence typically comprises a fence energizer to generate high-voltage electrical pulses which are propagated down one or more conducting wires of the electric fence. In FIG. 1, four live wires are shown that are looped or connected together at their ends, namely Live Wire A, Live Wire B, Live Wire C and Live Wire D, with an Earth Wire also being provided. When a person or animal touches a conducting wire, a path to ground is created through the person/animal. The electrical potential (and possibly current) is monitored to detect if/when an electrical fault occurs. The electrical potential is typically raised to a level that is extremely painful to touch, so as to provide a very cost effective physical deterrent with alarm capabilities.
Advantageously, electric fences, unlike conventional fences, do not need to be strong enough to withstand an attempt to push through the fence. This advantage allows electric fences to be designed and constructed more simply than conventional fences. As a result, less material may be required and less maintenance may need to be performed than would be required for a conventional fence. This may often result in a significant cost savings over conventional fences. Thus, electric fences are favored by many landowners and have become increasingly popular. It may, however, not be desirable to excite a fence at a high voltage all the time i.e. a school playground.
If an electric fence breaks or is cut, a significant portion of the length of the fence may be de-electrified. This renders the entire de-electrified portion of electric fence virtually useless. Thus, an electric fence must be monitored closely and a fence break must be repaired as soon as possible.
The most straightforward method of monitoring an electric fence is to manually inspect the electric fence on a regular basis to verify that it is in working order. However, many electric fences are installed over rough terrain or over-grown areas which make it difficult to access portions of the fence for inspection. Moreover, the length of electric fences may extend thousands of metres, making the process of inspecting each point on such a fence exceedingly time-consuming. Thus, a need exists for a monitoring system which automatically alerts a user to a failure in an electric fence without requiring him to perform a manual inspection of the fence.
It is accordingly desirable to know the location of the damaged or failed section of the electric fence, to facilitate remedial action. A number of methods have been implemented to address this, including:    1. Mounting mechanical sensors on the fence, such as, vibration sensors, strain gauges on posts, taut-wire sensors, accelerometer sensors and other sensing devices along the perimeter and monitoring these sensors via a communication network.    2. Using multiple energizers to partition the perimeter covered by the electric fence into discrete electrical zones.    3. Using voltage (and/or current) sensing devices to monitor the electrical activity on the fence. If the voltage reading falls out of a specified range or the current reading falls rapidly, the sensing devices trigger an alarm.    4. In the case of optical fibers, using time domain reflectrometry (TDR) to locate where the optical properties of an optical fiber have changed due to deflection. TDR can, however, be used to locate short and open circuits on electric fence wires too, but TDR is technically challenging and typically requires expensive electronics to implement.    5. Using microphonic cable, infra-red beams, closed circuit television and microwave sensors, or any combination of these solutions, for monitoring and protecting the fence.
The primary disadvantage of the above techniques is that they are discrete technologies and are often unable to complement each other naturally. Some of these solutions can also be financially very costly to implement, for example TDR. Each of the above technologies has certain advantages and disadvantages. For example, a fence with vibration sensors alone may not be a deterrent to an intruder who does not understand that such a technology exists. Conversely, interacting with an electric fence can be a physically painful experience, and as such an electric fence can be a strong physical deterrent; however, the monitoring of electrical activity on the electric fence this does not take into account physical manipulation of the electric fence, for example, using an insulator (such as a wooden plank) to separate the wires of the fence, thereby enabling the intruder to climb through the fence. Also, for someone with a bit of knowledge, it is a relatively simple matter to bridge out a section of the fence electrically, and then cut the fence wires to gain entry through the fence without any alarm being raised.
A taut-wire system will now be described in more detail. In a taut-wire system, a taut-wire sensor is mounted on a post and clamped to a wire. Should the tension in the wire change, a deflection on the sensor occurs and an alarm is raised. In its simplest form, the taut-wire sensor can be a mechanical switch. More sophisticated taut-wire sensors utilise strain gauges and microprocessors implementing advanced processing algorithms, mounted in each sensor, which can compensate for gradual drift due to shifting corner posts, temperature effects, wind, or short duration deflection such as a soccer ball being kicked against the fence. False alarms can thus be drastically reduced by utilising such technology. As the strain gauges and electronics can be encapsulated in resin and a plastic housing, the harmful effects of lightning are far less significant.
An electric fence arrangement that includes the addition of taut-wire sensors results in a more secure barrier, but it still has shortcomings that need to be addressed. The present invention aims to provide a solution to address these shortcomings.
Thus, taut-wire sensors exist and are used for perimeter protection, and remote voltage and/or current sensors exist and have been used on electric fence barrier systems. The aim of the present invention is to combine these two technologies into a single sensor. The hardware and installation cost savings are significant